A position detection device including a light source, a light receiving element, and an operation unit has been conventionally known. The position detection device detects a position of an object to be measured that moves between the light source and the light receiving element along a predetermined direction (for example, a position of an end of the object to be measured, a slit position, etc.)
The light source such as a light emitting diode or the like, can irradiate light. The light receiving element such as a photodiode or the like, has a light receiving surface. The light receiving element converts the light that is irradiated on the light receiving surface to a current and the like, and thereby can detect the light. The operation unit detects a position of the object to be measured based on the current and the like that is output from the light receiving element.
Specifically, in such configuration, the amount of which the light irradiated from the light source is blocked by the object to be measured can be detected based on the amount of light that is detected by the light receiving element. Accordingly, the position of the object to be measured can be detected. Patent Document 1 (Japanese Patent Application Laid-Open No. 1998-209489) and Patent Document 2 (Japanese Patent Application Laid-Open No. 1989-36088) disclose this type of position detection device.
Patent Document 1 discloses a light receiving element with a configuration in which a light receiving surface is divided into two regions. Specifically, each light receiving region is a right triangle, and its hypotenuses are opposed to each other. In Patent Document 1, the position of an object to be measured is detected by individually detecting light that is irradiated on two light receiving regions and calculating (one output value)/(total output value of two regions).
In Patent Document 2, as with Patent Document 1, two triangular-shaped light receiving regions are arranged with its hypotenuses opposing to each other. In detail, the light receiving regions of Patent Document 2 have a trapezoid shape approximating to a triangle.